700R4 questions...

[-stew-]

1986 GMC 3/4 ton 4x4 170K miles. Fluid is black and smells like shit. Truck sat for five or six years. Feels real lazy on the 1-2 shift. Other wise feels strong on the 2-3, 3-4, and 4-3 shifts. Is it worth doing a fluid flush to try and save it? Can any adjustments be made? Or just get the thing rebuilt before it leaves me stranded? Any one on here that can do it feel free to shoot me a price for a rebuild.

[juicedimpss]

it wouldnt hurt to try changing the fluid/filter,thats the least expensive thing to try. If the fluid is burnt smelling,i think i would also look at a trans cooler that works also(especially if you put a fresh trans in it.)

[BR3W CITY]

700r4 has gotta have a trans cooler, that bastard hates heat. Also make sure to adjust the TV cable after you do the fluid and filter, so you don't have to worry about it later.

[-stew-]

It's got an external cooler, never looked to see how big. Is doing the fluid and filter a gamble like on some other trannys seem prone to be?

[BR3W CITY]

Hit or miss i suppose. Even if the fluid is nasty, as long as there aren't large metallic shavings on the magnet you should be ok. Some very fine metallic stuff is normal from the clutches wearing.

I don't think you'd really risk anything with fluid/filter and tv adjustment.

[team beater]

700r4 has gotta have a trans cooler, that bastard hates heat. Also make sure to adjust the TV cable after you do the fluid and filter, so you don't have to worry about it later.
X2 on adjusting tv cable. Fluid has probably been in it forever so dirty and smelling horrible are almost a given.

[pjturkey]

Once a trans has that many miles on it, doesn't changing the fluid actually make it worse? Or is that an old wives' tale?

You could try craigslist for a TH400 instead of having the 700R rebuilt......especially in a 4x4 3/4 ton truck. 700R's are poo....unless, of course, you dump a bunch of money into them.

[hotshift13]

Leave the fluid in, if it is crusty, that's what I've always been told. Couple times I changed it and trans goes out....

[FoxStang]

Leave the fluid in, if it is crusty, that's what I've always been told. Couple times I changed it and trans goes out....
Happened on my buddies truck, 2 weeks after the change the trans bit the dust. Someone told me that its because your removing all the worn off friction material that's now in the fluid, so once you drain it, all the friction material is gone too. Is this it, or does anyone have an explanation to why this happens?

[team beater]

If you bring it in to do a tranny flush, alot of shops do a reverse drain type of process that suck it from bottom up bringing all the shit on the bottom up, from my understanding this can fu(k your junk up. If you swap the fluid and filter, you are not really removing all of the fluid only about a 3rd or so. I have never had a problem changing fluid and filter, even on my jeep xj after 170,000 miles.

my .02

[wrath]

You can probably get away with changing the fluid and filter, but don't drain the whole system. The problem is that the new detergents will eat the glaze off the frictions and you'll have a slipping transmission.

Black fluid usually means it's burnt and contaminated. Burnt fluid is basically junk. Usually leads to hard part failure.

This truck has 100k on it. The first 63k it was a plow truck. I've run a lot of water through the transmission (I only ran the vent tubes to the cowl, little did I know I'd be fording water deep enough to roll the windows up so I didn't get a wet seat). I've also burnt the fluid once towing ~12,000lbs with it. It had a lot of engines in it ranging from the ragged out 42hp stock 305, a 230whp 350, a 430whp 383, and the 275whp 305 (7" vacuum at 900rpm, haha) it has in it right now. It's survived a lot of driveline breaks also. My point is, take care of it and it'll be alright.

And if the truck has been fscked with, check the TV cable adjustment. Not enough line pressure leads to heat.

http://truck.wrath.org/wheeling/fallbog_09-18-2004/brian.jpg

[Sprayaway Fox]

Changing the fluid IS a crapshoot. Seen it at a couple buddies shop. Some owner buys a high milage vehicle and asks to have it flushed. They tell them straight out if it takes a shit it isnt their fault.

If you change it and it works great. But if it goes to hell a couple thousand later you know why.

Its like changing gear oil thats been in there for a long time and it always spun posi. Then new fluid with LS lube and its a one wheel peel after. The dirt in there is taking up the slack from the worn clearance of the clutches.

If you do change it, good luck.